The present invention relates to a cistern having the functions of natural purification and plankton cultivation.
It is usually necessary for aquariums and the like to exchange old sea water or fresh water which is stained or tainted by ammonia and the like produced from bait, the excretion of fish, and dust and the like, for new sea water or fresh water in order for fish to inhabit the cistern or aquarium. Further, elaborate works are required for the exchange of sea water or fresh water, and therefore it has been very difficult to maintain and manage the aquariums and the like.